1. Technical Field
The apparatus and techniques described herein relate generally to power transmitters that can transmit power according to two or more wireless power standards.
2. Discussion of the Related Art
Wireless Power Transfer Systems (WPTS) are gaining increasing popularity as convenient way to deliver power without wires or connectors. WPTS currently under development in the industry can be separated in two major classes: magnetic induction (MI) systems and magnetic resonance (MR) systems. Both types of systems include a transmitting unit, sometimes referred to as a power transmitting unit (PTU), and a receiving unit, sometimes referred to as a power receiving unit (PRU). Typically, the PTU is used to wirelessly charge mobile devices such as smartphones, portable music players, tablets, and laptops, among other devices and applications. The mobile devices may include a PRU.
Inductive WPTS typically operate in an allocated frequency range of about one hundred to several hundred kilohertz using frequency variation as a power flow control mechanism. MI WPTS operate over short ranges (typically limited to about the diameter of a power transmit coil). In a MI WPTS, the magnetic fields decay exponentially from the power transmit coil, and are not radiated from the coil.
Resonant WPTS typically operate on a single resonant frequency using a tuned receiving antenna network and input voltage regulation to regulate output power. In typical applications, MR WPTS operate at a frequency of 6.78 MHz. At the higher frequency, electromagnetic power can radiate from the power transmit coil. Because a tuned receiving antenna is used, appreciable power transfer can occur over distances larger than the diameter of the power transmit coil.
With the introduction of WPTS into commercial products, different methodologies for power transfer using MR and MI systems evolved. Several industry committees such as the Wireless Power Consortium (WPC), the recently-merged Power Matters Alliance (PMA), and the Alliance for Wireless Power (A4WP), collectively A4WP/PMA, are working on developing international standards for consumer products based on wireless power transfer. The standards may include, for example, specifications on an amount of rectified current, voltage, and/or power generated at a PRU via the device's receiving coil and power rectification circuitry. Even though standards are being developed, MI and MR wireless power systems (operating at very different frequencies) are likely to continue to be implemented in different commercial products.